The present invention pertains to electronic equipment used in portable applications and, more specifically, to an interface between the system electronics in portable electronic equipment having dual battery packs that provides for the sequencing and switching of power to the system electronics and the battery packs.
The utility of electronic equipment used in portable applications, such as notebook computers, is often limited by the runtime that is possible when the equipment is battery powered. One common technique for extending the runtime of portable electronic equipment has been to provide for 2 distinct battery packs. Typically, the battery packs are removably mountable within a housing that contains the system electronics.
The use of two battery packs requires the implementation of a selector that connects one battery pack positive terminal to the system or charger while isolating the other pack from the system. The selector is traditionally implemented as a MOSFET switch array included in the system electronics.
Each battery pack in a traditional system usually includes a protection circuit and a pack control unit that together provide safety functions and control discrete MOSFETs that connect the pack cells to the pack positive terminal. In this implementation, the pack control unit identifies when the pack is connected to the system electronics, usually by measuring a voltage level, and enables the connection of the pack cells to the pack positive terminal by turning on the pack charge and discharge MOSFETs. A host processor within the system electronics follows a specific algorithm and connects one of the packs (when in dual pack mode) to the power bus that supplies the system.
This topology has been widely used in the industry with only minor variations in the implementation of the selector located on the system side. This architecture, however, has noted disadvantages, namely, the additional costs that are a direct result of the use of discrete MOSFET switches on the system side and additional power dissipation that also results from the use of such switches. Additionally, as a result of the additional voltage drop across the system side MOSFET devices used to implement the selector function, the runtime that is achieved from a battery pack is adversely affected.
It would therefore be desirable to provide an interface between the system electronics used in a portable electronic device that allows the use of battery packs and that avoids the above-described disadvantages of traditional architectures in battery powered systems.